Radio receiving apparatus



June 1, 1937.

s. A. STEVENS 2,082,187 RADIO RECEIVING APPARATUS Filed Nov. 24, 1933 INVENTOR SydneyA Stevens BY HIS ATTORNEY Patented June 1, 1937 UNITED STATES PATENT OFFICE 2,082,187 RADIO RECEIVING APPARATUS Application November 24, 1933, Serial No. 699,529 In Great Britain January 4, 1933 3 Claims.

This invention relates to radio receiving apparatus comprising arrangements for controlling the volume in accordance with the amplitude of the received carrier wave by impressing a unidirectional potential proportional to the rectified high-frequency current corresponding substantially to the unmodulated carrier wave on an electrode of a thermionic valve of the apparatus, as, for instance, the screen grid or control grid, so as to control the electronic emission from the cathode of the valve in accordance with the amplitude of the received carrier wave.

In the rectifier or detector circuits usually associated with radio receiving apparatus the current in the output circuit of the rectifier or detector comprises three components, viz. a direct current component, a low'frequency component corresponding to the modulations of the carrier wave, and a high-frequency component corresponding substantially to the unmodulated carrier wave. The high-frequency component has in some circuits been employed to produce a well known reaction effect and it is usual in certain circuits to connect a by-pass condenser across the output terminals of the rectifier or detector in order to by-pass as much of the high-frequency component as possible.

According to the principal feature of the present invention a rectifier, preferably of the dry surface contact type, is connected in series with the by-pass condenser across the output terminals of the rectifier or detector of the apparatus so that a unidirectional potential shall be built up across the rectifier which is proportional to the amplitude of the carrier wave, and this unidirectional potential is arranged to be impressed on an electrode of a thermionic valve of the apparatus so as automatically to control the volume.

In order that the invention may be readily understood several embodiments thereof will now be described by way of example, with reference to the accompanying diagrammatic drawing in which:

Figure 1 illustrates the invention as applied to a thermionic detector circuit of the well known leaky-grid type;

Figures 2 and 3 illustrate the modified forms of the circuit arrangements of Figure l, in which the rectifier connected in series with the by-pass condenser is arranged to give full-wave rectification;

Figure 4 illustrates the automatic volume controlling arrangements of the present invention combined with other volume controlling arrangements.

Referring first to Figure l, a condenser I bypassed by a high resistance 2 is interposed in the well known manner in the grid or input lead of the rectifying or detecting thermionic valve 3, the cathode 4 being connected to earth at 5 and the anode or plate 6 through a high-frequency choke 'l to the next stage of the apparatus. A variable reaction condenser 8 is connected directly to the anode or plate 6 in the usual way and a.

by-pass condenser 9 is connected directly across the output terminals of the valve, i. e., between the anode or plate 6 and the cathode 4. The reaction or regeneration circuit to which condenser 8 is connected is of the usual type and may comprise a regenerative coil connected between condenser 8 and ground and coupled with the input to the detector tube 3.

The high-frequency component of the output of the thermionic valve 3 owing to the presence of the high-frequency choke I can only flow in the reaction circuit comprising the reaction condenser 8 and in the by-pass circuit comprising the by-pass condenser 9, the values of the capacities of these two condensers being such that the low or modulation frequency component is choked thereby and passes through the high-frequency choke l to the next stage of the apparatus.

Interposed between the by-pass condenser 9 and the cathode 4 of the thermionic valve 3 is a half-wave rectifier or detector ID of the dry surface contact type such as is described in British patent specification No. 381,206 and the terminal of the said rectifier or detector which is connected to the by-pass condenser 9 is 7 also connected through a resistance Ii and conductor l2 to the screen or control grid of a thermionic amplifying valve (now shown in the drawing) preceding the thermionic detecting valve 3; the said grid may be connected to earth through a condenser l3 of small value adapted to conduct to earth any highfrequency currents which might otherwise be impressed on the grid. The rectifier or detector ii! is connected in series with the by-pass condenser in such a way that its low resistance direction is from anode or plate 6 to cathode 4, with the result that a negative unidirectional potential proportional to the high-frequency current corresponding substantially to the unmodulated carrier wave is built up across the rectifier l0, and impressed on the screen or control grid of the thermionic amplifying valve preceding the thermionic detecting valve 3.

It will be evident from the above description that only a relatively small modification of the usual detecting circuit of apparatus in general use at the present time is necessary in order to obtain automatic volume control in accordance with the present invention.

If desired a full wave rectifier l (Figure 2), I 2 (Figure 3) of the dry surface contact type may be employed in place of the half wave rectifier referred to hereinbefore.

Referring now to Figure 4, the automatic volume controlling arrangements described hereinbefore are combined with other automatic volume controlling arrangements in which a current is arranged to be passed through an asymmetric conductor M in one direction or the other depending upon the magnitude of the direct current component of the output circuitof the rectifying or detecting thermionic valve 3 of the apparatus, the potential difference across the asymmetric conductor I 4 being used to vary the potential applied to an. electrode or electrodes of one or more amplifiers of the apparatus so as automaticallyto control the volume of the output of the apparatus. When the present invention is combined with such other volume controlling arrangements the resistance ll, through which the half-wave rectifier or detector l6 of the dry surface contact type is connected to the screen or control grid of a thermionic amplifying valve preceding the thermionic detecting valve as described with reference to the first embodiment of the present invention, has that end which is connected to the said screen or control grid also connected through the asymmetric conductor I 4 constituted by a further half-wave rectifier or detector of the dry surface contact type to an adjustable contact l5 of a potentiometer resistance IS, the low resistance direction of this further half-wave rectifier or detector being from the resistance II to the potentiometer resistance I6 and current from a battery I8 is passed through the potentiometer resistance 16, another adjustable tap ll of which is connected to the cathode of the preceding thermionic amplifying valve referred to hereinbefore.

It will be evident that the invention is not limited to the particular circuit or circuits described hereinbefore which may be varied as desired to suit particular requirements without exceeding the scope of the invention.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. Radio receiving apparatus comprising a radio frequency by-pass condenser, a rectifier preferably of the dry surface contact type connected in series with said condenser across the output terminals of the detector of the apparatus for causing a potential drop across the rectifier which is substantially proportional to the amplitude of the carrier wave, a voltage divider energized from a source of unidirectional current, a connection from the junction between said condenser and said rectifier to a point on said voltage divider, a second rectifier included in said connection and poled in such a direction as to permit current to fiow into said divider, and means for impressing the potential drop existing across said second rectifier together with a potential drop from across a portion of said voltage divider on an electrode of a thermionic valve of the apparatus so as automatically to control the volume of the output thereof.

2. Radio receiving apparatus comprising a radio frequency by-pass condenser, a first rectifier connected in series with said condenser across the output terminals of the detector of the apparatus for causing a potential drop across the rectifier which is substantially proportional to the amplitude of the carrier wave, a second rectifier connected to the junction between said first rectifier and said condenser and poled in such a direction as to permit current to fiow away from said junction, means for introducing a biasing potential in series with said second rectifier, and means for impressing the combined potential comprising the potential drop existing across said second rectifier and said biasing potential on an electrode of a thermionic valve of the apparatus so as automatically to control the volume of the output thereof.

3. Radio receiving apparatus comprising a radio frequency by-pass condenser, a first rectifier connected in series with said condenser across the output terminals of the detector of the apparatus for causing a potential drop across the rectifier which is substantially proportional to the amplitude of the carrier Wave, a second rectifier connected to the junction between said first rectifier and said condenser and poled in such a direction as to permit current to flow away from said junction, means for introducing a biasing potential in series with said second rectifier, means for adjusting said biasing potential, and means for impressing the combined potential comprising the potential drop existing across said second rectifier and said biasing potential on an electrode of a thermionic valve of the apparatus so as automatically to controlthe volume of the output thereof.

SYDNEY ARTHUR STEVENS. 

